Natural Product Sciences
21(4) : 289-292 (2015)
http://dx.doi.org/10.20307/nps.2015.21.4.289
Two New Scalaranes from a Korean Marine Sponge Spongia sp.
Inho Yang1, Sang-Jip Nam2,*, and Heonjoong Kang1,3,*
1
School of Earth and Environmental Sciences, Seoul National University, NS-80, Seoul 151-747, Korea
Department of Chemistry and Nano Science, Global Top5 Program, Ewha Womans University, Seoul 120-750, Korea
3
Research Institute of Oceanography, Seoul National University, NS-80, Seoul 151-747, Korea
2
Abstract − Intensive chemical investigation of Korean marine sponge Spongia sp. has led to the isolation of two
new scalaranes. The planar structures of the new compounds 1 and 2 were determined through 1D and 2D NMR
spectral data analysis, while the relative stereochemistry of the compounds was determined based on the analysis
of 1H-1H coupling constants and NOESY spectroscopic data. Compounds 1 and 2 did not display any significant
biological activities on farnesoid X-activated receptor (FXR) in co-transfection assay.
Keywords − Scalarane, Sesterpenoid, Spongia sp., Korean sponge, Marine natural product
reported several scalaranes with FXR and cytotoxic
activities from two Korean sponge samples, Spongia and
Psammocinia sp. repectively.16 We further investigated
chemical components to discover new natural products
from Spongia sp., and have isolated two new scalaranes.
Herein, we describe the isolation and the structure elucidation of two new scalarenes 1 and 2 from Spongia sp.
Introduction
Marine sponge is well known as a rich source of
natural products with diverse chemical skeletons.1 Sesterterpene is a well-known chemical skeleton with the five
carbon isoprene building units and has been isolated from
diverse organisms including higher plants and fungus.2
Scalarane, belonging to the sesterterpene class of natural
products, is one of the marine exclusive chemical classes
mainly isolated from sponges and nudibranches.3 These
scalaranes have not been isolated from terrestrial organisms.
After the first report on this class of compound in 1972,4
more than 200 derivatives were reported until 20103 and
novel derivatives of scalaranes are still being reported.5
Early research revealed that these natural products possessed
antifeedant and antifouling activities,6,7 as well as other
variety of bioactivities had been reported such as cytotoxicity,8 anticancer,9 antibacterial,10 and anti-inflammatory.11 Biological activities of scalaranes were broadened
to include the inhibition of nuclear factor,12 protein tyrosine
phosphatase,13 and farnesoid X-activated receptor.14 Recent
efforts to discover novel marine natural products from
Korean sponges resulted in the isolation of new analogs
of scalarane compounds,15 also our research group has
Experimental
General experimental procedures – The optical rotation
was measured using a Rudolph Research Autopol III
polarimeter with a 5 cm cell. The UV spectrum was
recorded in a Scinco UVS-2100 with a path length of 1
cm. Infrared spectra were recorded on a Thermo Electron
Corporation spectrometer. NMR spectral spectroscopic
data were obtained using Bruker Avance 600 and 500
MHz spectrometer [CDCl3 (δH 7.26; δC 77.0) was used as
an internal standard]. HRFAB-MS data were measured on
a JEOL, JMS-AX505WA mass spectrometer.
Isolation – The genus Spongia sp. sponge was collected
by SCUBA at the Geoje Island, South Sea of Korea. The
frozen animal (3.4 kg, wet wt.) was lyophilized and the
dried specimen (600 g) was extracted with 50% MeOH in
CH2Cl2. The extract was partitioned between CH2Cl2 and
water layers. The CH2Cl2-soluble layer was evaporated in
vacuo and then partitioned between n-hexane and 90%
aqueous MeOH. The 90% aqueous MeOH layer was subsequently separated into 24 fractions with Sephadex LH20 column eluting with 50% MeOH in CH2Cl2. The
fraction 20 containing the mixture of 1 and 2 was further
*Author for correspondence
Sang-Jip Nam, Department of Chemistry and Nano Science, Global
Top5 Program, Ewha Womans University, Seoul 120-750, Korea
Tel: +82-2-3277-6805; E-mail: [email protected]
Heonjoong Kang, School of Earth and Environmental Sciences,
Seoul National University, NS-80, Seoul 151-747, Korea
Tel: +82-2-880-5730; E-mail: [email protected]
289
Natural Product Sciences
290
separated by reversed-phase HPLC (Phenomenex Luna
C-18(2), 250 × 100 mm, 2.5 mL/min, 5 μm, 100 Å, UV =
205 nm) eluting with 70% CH3CN in H2O.
o
Compound 1: colorless oil; [α]21
D −1 (0.002, CHCl3);
UV (MeOH) λmax (log ε) 210 (3.98) nm; IR (film) νmax
3393, 1761, 1682, 1236 cm−1; 1H NMR data, see Table 1;
13
C NMR data, see Table 1; LRFABMS m/z 401 [M + H]+;
HRFABMS m/z 401.3052 [M + H]+ (calcd for C26H41O3,
401.3056).
o
Compound 2: colorless oils; [α]21
D +8 (0.002, CHCl3);
UV (MeOH) λmax (log ε) 210 (3.96) nm; IR (film) νmax
3392, 1760, 1683, 1238 cm−1; 1H NMR data, see Table 1;
13
C NMR data, see Table 1; LRFABMS m/z 417 [M + H]+;
HRFABMS m/z 417.3017 [M + H]+ (calcd for C26H41O4,
417.3005).
Results and Discussion
The molecular formula of compound 1 was established
as C26H40O3 based on the analysis of HRFABMS data (a
Table 1. 1H and 13C NMR data of 1 and 2 in CDCl3.
1a
a
No.
1
δC, mc
40.1, CH2
2
18.8, CH2
3
42.2, CH2
4
5
6
33.5, C
56.6, CH
18.2, CH2
7
41.8, CH2
8
9
10
11
37.8, C
61.4, CH
37.8, C
17.3, CH2
12
40.7, CH2
13
14
15
37.8, C
54.7, CH
24.2, CH2
16
17
18
19
20
21
22
23
24
25
19-OMe
20-OMe
136.6, CH
127.0, C
57.9, CH
105.6, CH
171.0, C
21.5, CH3
33.5, CH3
16.5, CH3
16.6, CH3
15.5, CH3
57.9, CH3
2b
δH, m, J (Hz)
0.79, m
1.67, m
1.51, m
1.55, m
1.13, dt (9.4, 3.7)
1.39, m
COSY
2
HMBC
3, 23
1, 3
2
18.7, CH2
5
42.2, CH2
33.4, C
56.5, CH
18.2, CH2
0.78, m
1.40, m
1.51, m
0.96, dt (13.2, 3.5)
1.69, d (10.2)
5, 9, 24
41.8, CH2
8
37.3, C
58.5, CH
37.3, C
26.9, CH2
9, 18, 25
76.2, CH
44.0, C
47.7, CH
25.9, CH2
0.85, m
1.42, m
1.55, m
1.40, m
1.78, d (9.8)
1.30, m
2.07, m
2.31, dd (20.4, 4.0)
6.84, d (3.3)
15
14, 16
24, 25
16, 17
15, 18
18, 20
2.47, m
5.20, d (5.8)
19
18
19-OMe
0.78, s
0.84, s
0.84, s
0.91, s
0.76, s
3.56, s
δC, mc
40.4, CH2
22
21
143.1, CH
125.8, C
57.8, CH
204.0, CH
167.0, C
21.4, CH3
33.4, CH3
17.0, CH3
16.8, CH3
16.0, CH3
52.1, CH3
δH, m, J (Hz)
0.76, m
1.67, m
1.38, m
1.48, m
1.15, m
1.38, m
0.76, m
1.33, m
1.48, m
0.89, m
1.69, m
0.83, m
1.43, m
1.69, m
3.56, dd (11.8, 4.2)
1.33, m
2.21, d (11.4)
2.36, dt (20.2, 5.2)
7.28, m
3.58, s
9.86, d (3.6)
0.77, s
0.84, s
0.88, s
0.89, s
0.90, s
3.70, s
600 MHz for 1H NMR and 150 MHz for 13C NMR. b500 MHz for 1H NMR and 125 MHz for 13C NMR cMultiplicity was determined by
the analysis of 2D NMR spectroscopic data.
Vol. 21, No. 4, 2015
291
Fig. 2. Key COSY and HMBC correlations of 1.
Fig. 1. Chemical structures of 1 and 2.
pseudomolecular ion peak at m/z 401.3052 [M + H]+) and
on the interpretation of 13C NMR data. This molecular
formula indicated that 1 had seven degrees of unsaturation. The 1H NMR spectrum of 1 revealed the presence
of two downfield methine protons H-16 (δ 6.84, d, J = 3.3
Hz), H-19 (δ 5.20, d, J = 5.8 Hz), one methoxy group at
19-OMe (δ 3.56), and five methyl groups with all singlets
[H-21 (δ 0.78), H-22 (δ 0.84), H-23 (δ 0.84), H-24 (δ
0.91), H-25 (δ 0.76)]. The 1H and 13C NMR spectroscopic
data indicated the presence of carboxylic carbon [C-20 (δ
171.0)] and a tri-substituted double bond system [H-16 (δ
6.84), C-17 (δ 127.0) and C-16 (136.6)]. The α,βunsaturated-γ-lactone ring was constructed by the analysis
of long-range HMBC correlations. HMBC correlations
from H-16 (δ 6.84) to carbons C-18 (δ 57.9), and C-20 (δ
171.0), and from H-19 (δ 5.20) to a carbon C-20 (δ 171.0)
allowed the construction of the α,β-unsaturated-γ-lactone
ring moiety. Further interpretation of 2D NMR spectroscopic data revealed that 1 was based on a scalarane
skeleton, having a methoxy group at C-19 (Fig. 1). In
particular, HMBC correlations from five methyl singlets
to carbons (H-22/C-5, H-23/C-1, C-5, C-9; H-24/C-9, C14; H-25/C-12, C-14, C-18) were helpful to assign the
tetracyclic ring system of the scalarane skeleton (Fig. 2).
The HMBC correlations to C-5 (from H-3, H-7, H-21,
and H-23) and C-9 (from H-7, H-23, and H-24) in
combination with the interpretation of COSY cross peaks
of H-1 and H-3 constructed A and B ring of scalarane.
The presence of C and D rings was supported by HMBC
correlations from the methyl singlet H-24 to carbons C-9,
and C-14) and from the methyl singlet H-25 to carbons C12 and C-14, and by the COSY correlations between H15 and H-16, and between H-18 and H-19, respectively.
Lastly, tetrahydrofuran ring was established from HMBC
correlations from H-25 to C-18, from H-16 to C-20. The
interpretation of 1H-1H coupling constants and NOESY
correlations was deployed to determine the relative stereochemistry of compound 1. NOESY cross-peaks between
H-22 and H-23, H-23 and H-24 implied the axial orienta-
tions of C-22, C-23, and C-24. Finally, the α-configuration
of the methoxy group at C-19 was determined by correlations between H-19 and H-25 in NOESY spectra.
The molecular formula of compound 2 was established
as C26H40O4 based on the analysis of HRFABMS data (a
pseudomolecular ion peak at m/z 417.3017 [M + H]+) and
on the interpretation of 13C NMR data. The 1H NMR
spectra of the compound 2 were similar to those of
compound 1 except for the presence of aldehyde [H-19 (δ
9.86)] and oxygenated methine protons [H-12 (δ 3.56)].
The aldehyde group was positioned at C-18 based on
HMBC correlations from H-19 (δH 9.86) to carbons C-13
(δC 44.0), C-17 (δC 125.8), and C-18 (δC 57.8). The
position of a methyl ester at C-15 was also determined by
HMBC correlations of H-16 (δH 7.28) and H-20-OMe (δH
3.70) to C-20 (δC 167.0). Analysis of 2D NMR spectroscopic data allowed the planar structure of 2 to be established
as shown in Fig. 1. The coupling constant of H-12
(J = 11.8 Hz) indicated the axial oriented to the plane,
suggesting the β-orientation of the hydroxy group at C-12.
The FXR antagonistic effect and cytotoxicity of
compounds 1 and 2 were tested with published method,16a
but no significant antagonistic or cytotoxicity activities
were observed. Previously reported scalaranes with the
FXR antagonistic activity have hydroxyl/methoxy functional
group at C-12 and possess the substituted furan moiety in
the molecules.16a,b The presence of hydroxyl group at C12 and the furan ring in scalaranes could be crucial for
FXR inhibitory activity. The common functional group
with cytotoxic scalaranes is the oxygen atom at C-2316c,
however compound 1 and 2 possess a carbon atom at that
position. These structural differences may explain the no
bioactivities of the isolated compounds.
Acknowledgments
This research was supported by the Marine Biotechnology Program, the ministry of Oceans and Fisheries,
and by Suncheon Research Center for Natural Medicines.
I. Yang was in part supported by the BK21 program,
Ministry of Education, Korea.
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292
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Received June 30, 2015
Revised August 14, 2015
Accepted August 17, 2015